As an adsorbent capable of removing harmful ions from an aqueous solution, a silicotitanate has been known.
For example, Patent Literature 1 discloses a silicotitanate as an ion exchanger for removal of a radioactive substance in seawater and a production method for the same.
Patent Literature 1 discloses a silicotitanate containing niobium.
A raw material for the silicotitanate of Patent Literature 1 includes an organic alkoxy compound. Specifically, the raw material in Patent Literature 1 includes tetraethyl orthosilicate as a silica source, tetraisopropyl orthotitanate as a titanium source, and tetrapropylammonium bromide and tetrabutylammonium bromide as a structure directing agent. The silica source, the titanium source, and the structure directing agent are difficult to be obtained, and correspond to hazardous or deleterious materials. Therefore, vapor generated from them at high temperatures may cause explosion. Accordingly, the production method of Patent Literature 1 requires a reaction at low temperatures. However, the reaction rate is decreased at low temperatures and productivity declines, which is not preferred.
Patent Literature 2 discloses a method for producing a titanosilicate-type zeolite that is a separating agent capable of separating a gas or liquid mixture. However, a silica source, a titanium source, and a structure directing agent in Patent Literature 2 are tetraalkyl orthosilicate, tetrabutyl orthotitanate, and tetrapropylammonium hydroxide, respectively, which correspond to hazardous or deleterious materials. Vapor generated from these compounds and a mixture thereof at high temperatures causes a reaction tube to corrode. Therefore, use of a special production device such as stainless pressure-resistant reaction tube equipped with a Teflon (registered trademark) inner tube is required.
Patent Literature 3 discloses a crystalline silicotitanate CST-2 as an adsorbent for an aqueous solution including only cesium.
Patent Literature 4 discloses silicotitanic acid as an adsorbent for an aqueous solution including cesium and strontium.
Patent Literature 5 discloses an adsorbent for cesium or strontium including a crystalline silicotitanate that is different from a sitinakite structure and titanate.